1. Field of the Present Invention
The present invention relates generally to electric welders, and more particularly to the transformers used to convert a single phase high voltage power source to a high current power source for efficient resistance welding pulses in a robot arm welder.
2. Description of the Prior Art
Present art welding transformers generally step down line voltages of about 440-460 volts to a level of 5-7 volts by means of the turn ratios between the primary and secondary windings of a transformer in the ranges of 60:1 to 70:1. For many years, present art resistance welding transformers have been water-cooled by means of supplemental windings of cooling conduits wrapped around or through the device so that a cooling fluid can be circulated about the device to absorb heat and release it at a point remote from the transformer.
In U.S. patent application Ser. No. 416,376 for a transformer construction, the use of a cooling duct within the secondary winding of the transformer was first demonstrated as a practical invention. Usually, however, the cooling passages or conduits are separate from the windings of the transformer so they do not interfere with its operation. Thus, the heat is absorbed only after it has been conducted through a portion of the transformer and as a result, elevates the temperature of the primary and secondary windings and of the transformer core. Because of the possibility of areas of extremely high heat, so-called hot spots, transformer designers have heretofore down-rated the temperature capabilities of transformers so that the average of the so-called hot spots do not exceed the limitations of presently available insulation systems. In any event, the windings may still be subjected to large amounts of heat and high temperatures which can cause fatigue and possibly destruction of the insulation or the windings. A separate cooling system is more costly to produce, weighs more and does not convey heat away from the transformer as effectively as a cooling system which is integral with the windings themselves.
Limitations on the use of cooling passages integral with transformer windings primarily arise because of the need to electrically isolate the primary from the secondary windings of the transformer so that the effectiveness of the transformer is not reduced by conductivity of the coolant.
In U.S. patent application Ser. No. 416,376, systems of integrally cooling either the primary or the secondary windings were first demonstrated. There are, however, no welding transformers yet available in which both the primary and secondary windings are cooled simultaneously by the same coolant system.